Nitroparaffin fuel



Patented Jan. 16, 1951 NITROPARAFFIN FUEL John A. Hannum, Detroit,Mich., assignor, by

mesne assignments, to Borg-Warner Corporation, Chicago, 111., acorporation of Illinois No Drawing. Application September 12, 1945,

' 'Serial No. 615,917 7 4 Claims. (01. 52-1) l i This invention, incommon with that of my copending application Serial No. 687,213, filedJuly 30, 1946, for a Nitroparaffin Fuel, relates to a propellant in theform of a combustible fuel for a prime mover in which a part, if notall, of the oxygen required for combustion of the fuel is containedatnormal pressures and temperatures in far more concentrated form than isfound in previously'known liquid and gaseous fuel mixtures. Moreparticularly it relates to such a propellant to which a mechanical orphysical inhibitor has been added to decrease the violence of thereaction occurring and the flame temperature resulting when combustionof the fuel takes place.

In the development of prime mover fuels and propellants (the fuel andoxygen source considered together) certain researches have placedemphasis on the development of a self suiiicient or nearly selfsufficient propellant. By self sufiicient is meant a combination of fuelwith suiiicient oxygen to permit complete combustion of the fuel withoutthe addition of more oxygen from another source. type tend to burn withflame temperatures that are excessively high for the intended use; alsothey tend to detonate rapidly and have too high a rate of fiamepropagation for such uses.

A use of this kind of such a propellant is found in the gas turbine.Here the mechanical limitations of turbines and the materials from whichthey are made place definite limits on the aforementioned propellantcharacteristics. This is particularly true if it is desired to providefor a turbine a propellant that is self sufficient or nearly selfsumcientin oxygen in order to eliminate the air compressor now used withgas turbines.

- Gas turbines have become well known in the prime mover field, butheretoforehave been subject to a marked disadvantage in that it has beennecessary to providea compressor as an integral part of the unit inorder that the requisite amount of oxygen might be made available forcombusly true in the adaptation of gas turbines as a source of power todrive aircraft.

Gas turbines, as now built, have also been subject to a markeddisadvantage atthe time they Certain propellants of this 7 2 are startedin rotation. Like other types of prime movers, they are notself-starting. However, in the case of such a turbine, the auxiliarypower required to place the unit in rotation to perform work is muchgreater than, for example, witli'an Otto cycle internal combustionengine. In the case of ,a gas turbine, power in an amount approximatingthirty per cent of the output of the unit is required to place the samein operation.

Even after a gas turbine of the presently known type is in operation atits normal working efiiciency there is a marked disadvantage to its.use. If the entire output'of the turbine be considered as one hundredper cent, it is very possible that under certain types of use only tenper cent of this output will be devoted to performing work, namely toaccomplish the function for which the turbine is intended. Thebalance'of the output of-the unit is required to compress fromatmospheric pressure the air that is required for cornbustion of thefuelwhich drives the turbine.

It has been recognized that if a gas turbine could be provided with asuitable fuel which eliminated the foregoing disadvantages, its field ofapplication would be considerably broadened. Fields in which it now hasutility would be expanded and other fields in which its use is-not nowpractical would be opened. At the present time gas turbines have foundsome use as sta-.

tionary auxiliary equipment in power plants The use of gas turbines todrive jet propelled aircraft with oxygen received from the atmospheresubjects the aircraft to a very marked ceiling limitation. As anaircraft rises higher and higher from the surface of the ground, theamount of oxygen in the surrounding atmosphere available for combustion'of the fuel becomes more limited. This fact, together with the requirement for compression of the air, even' at ground levels, to supplythe requisite oxygen, is a definite limiting factor to the ceilingavailable with aircraft using this type of propulsion.

If it were possible to provide a propellantfor driving gas turbines orfor similar uses which in itself contained all, or a required majorpart, of the necessary materials for combustion, the necessity forrelying on the supply of air from 'the surrounding atmosphere would" beeliminated or greatl decreased. In effect this would make possibleflight into the stratosphere and beyond because the propelling unitcarried with in itself both the fuel and the oxygen necessary for itscombustion.

I have invented a propellant to meet the needs outlined above thatconsists of a mixture of a fuel such as 'nitromethane, a concentratedoxidizing agent in which the oxygen for combustion is in combined form,e. g., tetranitromethane and a mechanical or physical inhibitor tocontrol the combustion. It is to be made clear that such a propellant isnot limitedin its use to gasturbine propulsion. Although even wi outinhibitors, such propellants have been found to be.

eminently satisfactory for some purposes and under certain conditions,in the present pro.- pellant I prefer to use a mechanical or physical,as distinguished from a chemical, inhibitor.

Generally the present invention is concerned with re usin th f a tem a ute of lame propa ati n a d d on ch teristicsof propellants such asexemplified above by adding water or other inert liquids, or solids,directlyfin the propellant to act as a mechanical oriphysical inhibitor.A chemical inhibitor does t' act to reduce the flame temperature of a prpeilant in which it is mixed. A mechanical inhibitor acts by absorbingheat hrquehw .til a n or by f e hani interference to the combustion of.the fuel and "'dant'. Water and like inhibitors are not in al misciblewith propellants of the kind in-- rested and thu i s e ue preferable tmahe a stable emulsion of all the ingredients of the propellant. Theadvantage of this is that pr pellant ingredients do not tend tosepas ate.1m: I

It has been an object of the present invention to: provide amechanically inhibited propellant which would combine within itself there uisite ue as Well. a Oxy e n a @Qm ned f r to enable completecombustion of all the fuel to take place without need for supplyingfurther oxygen. Another object of theinvention has been to provide apropellant as indicated in which all theingredients are made into astable emr lsion by addition of an emulsifying or dispersing agent.Other objects of the invention willbecome apparent from the followingspeciration h le he o el e u e umm i ed ntl 'le eims- A stoichiometricmixture of nitromethane and tetranitromethane burns atapproximately3000" F. This temperature is too high to be handled in prime movers ofthe kind contemplated by this invention. This is because the physicalcharacteristics of their component parts are such that prime movers arenot capable of Withstand?- injg temperatures of this degree. On theother hand itiis desirable to burn a fuel at as high a temperature aspermissible because the thermo-. dynamic efficiency increases as thetemperature ofcombustion is raised. There are uses for a direct mixtureof tetranitromethane and nitro- Inethane, but the present invention inone form directed to a propellant using these materials when their flametemperature is limited to approximately 3500 F. This is the approximateflame temperature, that is reached during the n o e ha e a atmos heriir.

we r h s a r mechani al s sh d em. a im eL- n1i c r-- ave mem t m eret ras eted,

aware may 4 mechanically to impede or inhibit the combustion of thepropellant and its oxidizing agent. This is due largely to the fact thatwater has a high heat of volatilization and a high specific heat as aresult of which it acts rapidly to conduct heat away from the flamepoint. There is thus a consequent reduction intemperature at the pointof Combustion. It will be understood that other suitable chemicallyinert substances may he used as physical or mechanical inhibitors aslong as they produce the same end result as that described above.

An ideal mixture of the components of a propellant using nitromethanewould consist of the following materials in the indicated proportions byweight:

-Nitro rnethane, 35% approximately Tetranitromethane, 30% approximately"Water, 35% approximately While the percentages of the components in thepropellant listedabove illustrate one preferred form of the invention itis to be understood that the invention is not limited to this mixture.Considerable latitude in percentages is possible without departing fromthe scope of the disclosure. Propellants mixed in proportions by weightand falling within the bounds of the following tabu lation are to beconsidered as part of my invention:

Nitromethane, 55.5% to 30% Tetranitromethane, 44.5% to 25% Inhibitor,trace to 45% Generally speaking the less water or other inhibitorsupplied to the mixture, the higher the flame temperature andaccordingly the propellant will consist of the above constituents invarious proportions dependin upon the flame tempfirature that isdesired. The amount of inhibitor, for example, Water, required may becalculated in each case by a consideration of the desired flametemperature and the number of heat units the water can remove as it isvolatilized and separated outfrom the other ingredients. Also, thepercentages of nitromethane and tetranitromethane set out above are notcritical as defining the limits of this invention. For certain uses itwill be desired to alter these percentages for instance, when part ofthe oxygen for combustion is supplied from an additional source such asair. 7 V

A mixture of the type set forth having the proportions of fuel andoxidizing agent given above preferably should be made into a stableemulsion. This may be done by addition to the propellant mixture of adispersing or emulsifying agent. The result is a liquid in which theingredients are not subject to separation. To accomplish this thereshould be added a small amount, preferably approximately one percent(1%) by weight of the total mixture, of a triethanolamine soap.Specifically this emulsifying agent may be triethanolamine stearate.

Such a propellant as indicated above then pref! erably consists of thefollowin ingredients mixed in substantially the indicated percentages byweight if the fuel is nitromethane:

- ib s pr po s are illustrative and it is .con.-;

templated that the ingredients used in varying proportions as set outbelow also lie within the scope of this invention.

It is not intended to limit the invention to the specific proportionsindicated. Reasonable ranges of percentages are considered as comingwithin the scope of the present invention. These ranges are dependentupon two factors. One of them is the degree of self sufficiency of themixture of fuel and oxidizin agent with respect to oxygen from anothersource. Thus if air is to be supplied to the mixture in addition to theoxidizing agent,

less tetranitromethane is required than. otherwise would be indicated.The other factor is the degree to which it is desired to inhibit thepropellant and, for example, lower its flame temperature.

Accordingly, my invention is to be construed as including the followingpropellants made up of ingredients mixed in the following percentages byweight:

Nitromethane, 55.5% to 29% Tetranitromethane, 44.5% to 24% Inhibitor,trace to 45% Emulsifying agent, trace to 2% From the foregoingdescription it will be seen that I have provided a prime moverpropellant that may be self contained to any desired degree as far asfuel and oxygen are concerned and to which a mechanical or physicalinhibitor has been added so that it is safe to handle with a controlledrate of combustion r flame propagation and with a controlled flametemperature. Essentially the present invention covers a fuel, a sourceof oxygen in combined form, a mechanical or physical inhibitor and insome cases a dispersing agent. Although the mixtures and percentageslisted herei are, considered, the preferred forms of the invention,other mixtures and percentages that fall within the range of equivalentsproperly ascribed to this disclosure are a part of my invention. 1

It is intended that the patent shall cover, by suitable expression inthe appended claims, whatever features of patentable hoveltyreside inthe invention.

I claim:

1. A prime mover propellant containing as essential ingredients a.mixture of the following ingredients in approximately the indicatedpercentages by weight:

Tetranitromethane, 30% Nitromethane, 35% and the balance Water as amechanical inhibitor 2. A prime mover propellant containing as essentialingredients a mixture of the following ingredients in approximately theindicated percentages by Weight:

Tetranitroinethane, 29% Nitromethane, 35%

, A triethanolamine soap, 1 and the balance Water as a mechanicalinhibitor 3. A prime mover propellant containing as essentialingredients a mixture of the following ingredients within the indicatedranges of percentages by weight:

Nitromethane, 55.5% to 30% Tetranitromethane, 44.5% to 25% Water, traceto 4. A prime mover propellant containing as essential ingredients amixture of the following ingredients within the indicated ranges ofpercentages by weight:

Nitromethane, 55.5% to 29 Tetranitromethane, 44.5% to 24% Water, traceto 45% Dispersing agent, trace to 2% JOHN A. HANlN'UM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

3. A PRIME MOVER PROPELLANT CONTAINING AS ESSENTIAL INGREDIENTS AMIXTURE OF THE FOLLOWING INGREDIENTS WITHIN THE INDICATED RANGES OFPERCENTAGES BY WEIGHT: